This invention relates, generally, to connection oriented communications networks and, more particularly, to aggregation of connections onto higher level containers whereby network level fairness in distributing available bandwidth to the connections is achieved.
Connection oriented communications networks are well known and in general are characterized by the establishment of a circuit connection through the network over which respective end-systems can communicate. Such networks include the public switched telephone network (PSTN) which traditionally has utilized physical circuit switching technology, and packet based networks which utilize virtual circuit switching technology. Examples of packet based network technologies supporting virtual circuits are asynchronous transfer mode (ATM), frame relay (FR), and multi-protocol label switching (MPLS).
In particular, ATM is rapidly becoming the technology of choice for broadband digital communications, as it provides various levels of service guarantees and therefore is well suited to multimedia applications including voice, video and data. The packet used in ATM has a fixed length and is known as a cell. Furthermore, ATM supports two levels of virtual circuit connections: a first or lowest level connection is a virtual channel (VC), and a second or higher level connection is a virtual path (VP) comprising multiple virtual channels that are effectively abstracted by the VP.
The ATM cell has a length of 53 bytes as its basic unit. The first five bytes of every cell are allocated to the ATM layer overhead more commonly referred to as the header. The remaining 48 bytes are used to transport the ATM cells payload. Special cells, referred to as Resource Management (RM) cells, can be used to perform different control functions for a connection. The specific purpose of an RM cell is identified using a protocol identification field.
The ATM Forum""s Traffic Management Specification version 4.0 has established five categories of service relating to ATM traffic. The five categories of service are: constant bit rate (CBR); real time variable bit rate (rtVBR); non-real time variable bit rate (nrtVBR); unspecified bit rate (UBR); and available bit rate (ABR). Each service provides a different level of Quality of Service (QoS) using different traffic descriptors.
The ABR service category incorporates an integrated flow control loop using resource management (RM) cells with a specific protocol ID field. This RM cell collects congestion information at each network element and is returned to the source where the information is used in controlling the source send rate. The use of RM cells for the control of CBR, VBR and UBR service connections is at present undefined in the ATM Forum Traffic Management Specification version 4.0. However, RM cells are permitted on these connections.
With respect to the two levels of connections in ATM, a VC refers to a logical connection between two end points for the transfer of ATM cells, while a VP represents a logical aggregation of VCs that typically have the same termination point. Through the utilization of a VP, numerous (up to 64,000, for example) VCs can be combined into a single VP. Cells are identified using a combination a virtual connection identifier (VCI) and a virtual path identifier (VPI). Cells that are aggregated onto a VP all share the same VP value. When cells are switched by a VP switch, the switch only considers the VPI and does not generally keep any VC level information. VCs that are aggregated onto a VP can have a different service category than the one of the VP as long as the VP provides a better quality of service than the underlying VCs. Virtual path connections are beneficial at the core of a network where the VP is used extensively to reduce the number of connections and to simplify network management, thus increasing scalability.
Over the past number of years considerable effort has been devoted to designing complex traffic management schemes which attempt to achieve a fair sharing of network bandwidth between VCs. Network level fairness wherein each VC gets a weighted fair share of the available bandwidth, is an important aspect of traffic management. In this context xe2x80x9cweightingxe2x80x9d is a proportion or ratio of the available link bandwidth that is allocated to a particular VC or VP at a given instant.
The aforementioned ATM Forum Traffic Management Specification version 4.0 (TM4.0) establishes criteria respecting various service related aspects of ATM traffic including service categories and quality of service guarantees. Scheduling mechanisms are not specified in TM4.0 however, these mechanisms are key in providing fair access to bandwidth. One example of a scheduling mechanism that provides fair access to available resources is described in xe2x80x9cA self-Clocking Fair Queuing Scheme for Broadband Applicationsxe2x80x9d by S. J. Golestani, INFOCOM 1994, June 1994. With such a scheme, the system can instantaneously allocate available bandwidth between different queues proportional to a weight associated with each queue.
There remains, however, a fairness and efficiency issue arising when using VPs and switching VPs. VPs are set up with a specific set of traffic descriptors prior to having VCs dynamically added and removed onto it. In the VP switches there is no knowledge of how much traffic is aggregated at a given instant on a given VP aggregation point. Accordingly, the bandwidth is allocated proportionally to the VP traffic descriptor without any consideration of the amount of traffic flowing on each VP at a given time. For example, assuming that two VPs are set up with the same traffic descriptors, but at a given instant, one VP aggregates a load that is double the load of the other VP, both VPs will be allocated the same amount of bandwidth in the VP switch, and the VCs aggregated on the VP with the largest load will received a lower share of the available bandwidth than would be if there were no VPs used.
Therefore, a scheme that improves the network level fairness when using VPs such as in an ATM core is desirable.
It is an object of the present invention to provide a new and improved methodology for distributing available bandwidth to connections in a communications network.
Therefore, in accordance with a first aspect of the present invention, there is provided a system for improving network fairness amongst virtual path connections in a connection oriented network. The system comprises: aggregation means for aggregating virtual circuit connections onto virtual path connections; means associated with the aggregation means for selectively sending a VP resource management cell with load information respecting the virtual path; virtual path switching means for routing the virtual path connections to a designated destination; and means in the VP switching means to intercept the resource management cell and to use the load information therein to allocate a fair share bandwidth to the virtual path.
In accordance with a second aspect of the present invention, there is provided a method of improving network fairness in a communication network utilizing virtual circuit connections aggregated onto virtual path connections for carrying traffic across the network. The method comprises: providing aggregation means to aggregate VC connections onto VP connections; providing means associated with the aggregation means to include VP resource management cells on the virtual path connection, the resource management cells including load information; providing switching means to route the VP traffic through the network; and providing means in the VP switching means to intercept the load information and to allocate bandwidth to the VP in accordance with the weight information.